Create a mashup which uses Web services such as Google or Yahoo maps APIs to create an interactive Web sites. For example, the map APIs provide a way to display a map on the Web page, with other information overlayed on the maps. You could implement a restaurant recommendation system, with users contributing information about restaurants such as location, cuisine, price range, and ratings. Results of user searches could be displayed on the map. You could allow Wikipedia-like features such as allowing users to add information and edit information added by other users, along with moderators who can weed out malicious updates. You could also implement social features, such as giving more importance to ratings provided by your friends.